lkml.org 
[lkml]   [2018]   [May]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v3 2/3] ACPI: ensure acpi_parse_entries_array() does not access non-existent table data
On Tue, May 1, 2018 at 2:39 AM, Al Stone <ahs3@redhat.com> wrote:
> For ACPI tables that have subtables, acpi_parse_entries_array() gets used
> to step through each of the subtables in memory. The primary loop for this
> was checking that the beginning location of the subtable being examined
> plus the length of struct acpi_subtable_header was not beyond the end of
> the complete ACPI table; if it wasn't, the subtable could be examined, but
> if it was the loop would terminate as it should.
>
> In the middle of this subtable loop, a callback is used to examine the
> subtable in detail.
>
> Should the callback function try to examine elements of the subtable that
> are located past the subtable header, and the ACPI table containing this
> subtable has an incorrect length, it is possible to access either invalid
> or protected memory and cause a fault. And, the length of struct
> acpi_subtable_header will always be smaller than the length of the actual
> subtable.
>
> To fix this, we make the main loop check that the beginning of the
> subtable being examined plus the actual length of the subtable does
> not go past the end of the enclosing ACPI table. While this cannot
> protect us from malicious callback functions, it can prevent us from
> failing because of some poorly constructed ACPI tables.
>
> Found by inspection. There is no functional change to existing code
> that is known to work when calling acpi_parse_entries_array().
>
> Signed-off-by: Al Stone <ahs3@redhat.com>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: Len Brown <lenb@kernel.org>
> ---
> drivers/acpi/tables.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> index 4a3410aa6540..82c3e2c52dd9 100644
> --- a/drivers/acpi/tables.c
> +++ b/drivers/acpi/tables.c
> @@ -274,8 +274,7 @@ acpi_parse_entries_array(char *id, unsigned long table_size,
> entry = (struct acpi_subtable_header *)
> ((unsigned long)table_header + table_size);
>
> - while (((unsigned long)entry) + sizeof(struct acpi_subtable_header) <
> - table_end) {
> + while ((unsigned long)entry + entry->length <= table_end) {
> if (max_entries && count >= max_entries)
> break;
>
> --

This breaks the CPU enumeration on my Dell XPS13 9360 (possibly among
other things), so I'm dropping it. I can send you acpidump output
from that machine if need be.

Thanks,
Rafael

\
 
 \ /
  Last update: 2018-05-15 19:20    [W:0.157 / U:2.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site